This grant proposal is directed toward two fundamental objectives: 1) determining the short- and medium-term effects of diet on the metabolic interrelationship(s) of triglyeride-rich lipoproteins (Chylomicrons and very low density lipoproteins (VLDL), and high density lipoproteins (HDL2 and HDL3); 2) determining the effect of dietary fat saturation on plsma levels, distribution, and structure of high density lipoproteins and other lipoproteins. These objectives will be approached through two sets of studies: Short term, acute studies (0-24 hour) will focus on the capacity of individuals with various plasma HDL levels and HDL2/HDL3 ratios to metabolize oral fat loads of varying saturation. The distribution of HDL and VLDL subfractions will be determined by zonal ultracentrifugation. Pyrene excimer fluorescence and spin label paramagnetic resonance will be used to monitor the changes in the microscopic fluidity of chylomicrons and VLDL effected by fat loads of different saturation. A probable relationship between the microscopic fluidity of VLDL and its rate of catabolism, in vivo and in vitro, will be explored. Medium term (2 week) studies will examine the effect of an ad libitum diet, highly polyunsaturated diet, highly saturated diet, and the "Help Your Heart Eating Plan" diet on the plasma lipoprotein levels, distribution, composition, and microscopic fluidity in normal adult subjects (5 males and 5 females) and subjects with Type II and Type III Hyperlipoproteinemia (2 each). The result of these studies should provide a clearer view of the effect of dietary manipulation on human HDL; and indirect information about the relationship of diet to cardiovascular disease and atherosclerosis.